Several different types of visible light emitting semiconductor lasers based upon the (Al.sub.x Ga.sub.1-x).sub.0.5 In.sub.0.5 P materials system are currently being developed. In general, however, the performance of such lasers is limited by relatively weak electron confinement as compared to infrared AlGaAs diode lasers. This problem becomes more acute as laser output power increases, as the emission wavelength becomes shorter, and/or as the laser's operating temperature increases.
A major result of the weak electron confinement is electron heterobarrier leakage. Heterobarrier leakage is caused by thermally-excited electrons surmounting the confining heterobarrier at the interface between the cladding layer and either the active region in a double heterostructure laser or the confining region in a quantum well laser having a separate confinement heterostructure. In either case, electrons which have leaked into the p-cladding layer contribute to leakage current by diffusing and drifting toward the p-contact. Since hole mobilities in an AlGaInP cladding layer are relatively low, the drift component can be significant. Furthermore, since the confining potentials in an AlGaInP heterostructure are less than those in an AlGaAs system, the electron leakage current can be a much larger fraction of the total diode current.
Because high heterobarrier leakage in a semiconductor laser increases the temperature sensitivity of the laser's threshold current and reduces the laser's maximum operating temperature, semiconductor lasers based upon the (Al.sub.x Ga.sub.1-x).sub.0.5 P materials system having reduced heterobarrier leakage would be beneficial.